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BLISS-36 Release 4A(236) For TOPS-20: Release Notes
7-AUG-1989
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 2
CONTENTS
1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . 3
2.0 NEW FEATURES . . . . . . . . . . . . . . . . . . . . 3
3.0 COMPILER PERFORMANCE IMPROVEMENTS . . . . . . . . . 3
3.1 Compiler dynamic memory use <36> . . . . . . . . . 3
4.0 CODE QUALITY IMPROVEMENTS . . . . . . . . . . . . . 3
4.1 Move merging <All> . . . . . . . . . . . . . . . . 3
4.2 Comparison merging <All> . . . . . . . . . . . . . 3
4.3 Bit test merging <All> . . . . . . . . . . . . . . 4
5.0 CORRECTIONS . . . . . . . . . . . . . . . . . . . . 4
5.1 ENABLEs and initialized LOCALs <All> . . . . . . . 4
5.2 Relation between difference and constant <All> . . 4
5.3 Frame pointer of main program <36> . . . . . . . . 4
5.4 Incorrect error messages <All> . . . . . . . . . . 5
5.5 PRESET with address of LOCAL variable <All> . . . 5
5.6 Multiple END statements in assembly listing for
main routine <36> . . . . . . . . . . . . . . . . 5
5.7 Spurious "symbol previously declared" messages
<All> . . . . . . . . . . . . . . . . . . . . . . 5
5.8 Compiler fails when installed in an SFD <36>
(TOPS-10) . . . . . . . . . . . . . . . . . . . . 5
5.9 Illegal UUO after fatal error <36> (TOPS-10) . . . 5
5.10 Flow analysis failure <All> . . . . . . . . . . . 6
5.11 Bad code for the MOD operator <All> . . . . . . . 6
5.12 Cross-reference fixes <All> . . . . . . . . . . . 6
6.0 MISCELLANEOUS . . . . . . . . . . . . . . . . . . . 6
7.0 CHANGES TO UNSUPPORTED TOOLS . . . . . . . . . . . . 6
8.0 CHANGES TO UNSUPPORTED SOFTWARE . . . . . . . . . . 6
8.1 XPORT - Transportable BLISS Programming Tools . . 7
8.2 SIX12 - BLISS Symbolic Debugger . . . . . . . . . 7
9.0 RESTRICTIONS . . . . . . . . . . . . . . . . . . . . 7
10.0 KNOWN BUGS . . . . . . . . . . . . . . . . . . . . . 9
11.0 FOR FURTHER HELP . . . . . . . . . . . . . . . . . . 9
12.0 COMPONENTS . . . . . . . . . . . . . . . . . . . . 10
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 3
1.0 INTRODUCTION
This document provides information pertaining to BLISS-36 Version
4A(236).
2.0 NEW FEATURES
Version 4.1 of the BLISS language is upward compatible with Version
4.0. Each change documented in this section includes a flag such as
<16> indicating which compilers it applies to.
3.0 COMPILER PERFORMANCE IMPROVEMENTS
4.0 CODE QUALITY IMPROVEMENTS
4.1 Move merging <All>
Assignments from consecutive fields of a source area to consecutive
fields of a destination area now generate a single move instruction.
Also, assignments of literals to consecutive fields of a destination
area should now generate a single move instruction. Thus, "A<3,3> =
.B<3,3>; A<6,4> = .B<6,4>" will be turned into "A<3,7> = .B<3,7>",
and "A<3,3> = 1; A<6,4> = 3" will be turned into "A<3,7> = 19".
4.2 Comparison merging <All>
Similarly, ".A<3,3> EQL .B<3,3> AND .A<6,4> EQL .B<6,4>" will now be
turned into ".A<3,7> EQL .B<3,7>", and ".A<3,3> EQL 1 AND .A<6,4> EQL
3" will be turned into ".A<3,7> EQL 19". The corresponding
transformation for ORs of NEQs is also performed.
4.3 Bit test merging <All>
Multiple bit tests on a single word will be turned into a mask test.
For example, ".A<4,1> OR .A<6,1>" will be turned into "(.A AND %X'50')
NEQ 0".
5.0 CORRECTIONS
This section describes changes to correct problems which resulted in
compiler failures or in the generation of incorrect code.
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 4
5.1 ENABLEs and initialized LOCALs <All>
Initialized local variables which are used in an ENABLE declaration
are now zeroed before the handler is enabled, and initialized
afterwards. This allows handlers to determine whether an exception
occurred during initialization or during routine body execution.
Previously, BLISS-32 was doing the initialization before the ENABLE;
BLISS-36 and BLISS-16 were doing the ENABLE before the initialization,
but weren't zeroing the variables first.
5.2 Relation between difference and constant <All>
A test of the form "<expr1> - <expr2> <relation> <const>" was being
incorrectly converted to "<expr1> <relation> <expr2> + <const>". For
example, "IF .A - .B GTR 0 THEN" was converted to "IF .A GTR .B THEN".
This looks plausible, but certain overflow conditions invalidate it.
The only form of this optimization allowed now is "<expr1> - <expr2>
EQL/NEQ 0" => "<expr1> EQL/NEQ <expr2>".
5.3 Incorrect error messages <All>
Incorrect error messages were generated when the compiler was unable
to read a library or require file. Also, the error message "PLIT or
INITIAL size exceeds implementation limits" was not generated for
TOPS-10 BLISS-36. These have been fixed.
5.4 PRESET with address of LOCAL variable <All>
When a local variable name occurred in a PRESET list, the compiler
generated an EXTERNAL reference for that name. For example, "LOCAL A,
B : BLOCK [3] PRESET ([0, 0, 32, 0] = A)" would result in "Undeclared
global symbol A" when it was linked. This has been fixed.
5.5 Spurious "symbol previously declared" messages <All>
With /CHECK=REDECLARE, a spurious "symbol previously declared in an
outer block" message was generated when a symbol was declared EXTERNAL
in an outer block, and GLOBAL in an inner block. This has been fixed.
5.6 Flow analysis failure <All>
The compiler would fail in the flow analysis phase when confronted
with certain extremely complex patterns of common subexpression usage
(involving nested IFs within LOOPs within IFs). This has been fixed.
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 5
5.7 Bad code for the MOD operator <All>
The compiler would sometimes generate code for the MOD operator that
would compute a result with the wrong sign. In particular, the
compiler would sometimes compile "(-x) MOD (-y)" as "x MOD y". This
will now be compiled as "-(x MOD y)".
5.8 Cross-reference fixes <All>
Several minor problems with the output produced by the
/CROSS_REFERENCE qualifier have been fixed.
6.0 MISCELLANEOUS
7.0 CHANGES TO UNSUPPORTED TOOLS
NOTE
This section describes components of the
BLISS V4 release that are not supported
by DIGITAL. These items are provided
only as a service to our users.
See the User's Guide for information concerning these tools.
8.0 CHANGES TO UNSUPPORTED SOFTWARE
As a courtesy to our users, some unsupported development tools are
shipped with the BLISS distribution.
8.1 XPORT - Transportable BLISS Programming Tools
A maintenance release of XPORT appears in the version 4A release.
8.2 SIX12 - BLISS Symbolic Debugger
Included in this release is a machine-readable manual - SIX12.MEM
which serves as a reference manual for the debugger.
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 6
9.0 RESTRICTIONS
This section summarizes restrictions with the V4A(236) release. Where
possible, temporary solutions are described.
PROBLEM: The following code fragment
d = 0;
.....
WHILE .d NEQ 0 DO
BEGIN
....
x = 66 / .d; ! Assume "d" never written
...
IF .y THEN EXITLOOP
END
will cause a zero-divide exception at execution time when
compiled using normal optimization. The compiler believes
that the expression "66/.d" is loop invariant and moves the
computation out of the loop.
SOLUTION: This is a restriction in V4A. In this particular case, the
expression could be rewritten as:
WHILE 1 DO
BEGIN
.....
IF .d EQL 0 THEN EXITLOOP;
....
x = 66 / .d;
.....
END;
In this case, the expression cannot be moved out of the
loop.
PROBLEM: Incorrect code generated for structure definitions of the
form:
STRUCTURE BAD[I,P,S]= [%UPVAL]
(IF .I THEN BAD ELSE BAD + .BAD<16,16>)<P,S>;
OWN X: BAD[];
LOCAL T;
T = .X[.T,0,12];
"X" is loaded into a register in the THEN-branch, but the
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 7
ELSE-branch uses the register without loading it.
SOLUTION: This is the result of a design flaw in the way structure
references are expanded. BLISS semantics guarantee that a
structure actual-parameter is evaluated only once. This is
implemented by treating the first occurrence of a structure
formal as if it was a BIND declaration. The other
occurrences of the structure formal are then treated as if
they were uses of the "imaginary" bind-name. This choice of
implementation fails when the first occurrence of the
structure formal is in conditional flow! The problem can be
avoided by insuring that the first occurrence of each formal
is outside of conditional flow. The example structure
should be written as:
STRUCTURE GOOD[I,P,S] = [%UPVAL]
(GOOD; IF .I THEN GOOD ELSE GOOD+.GOOD<16,16>)<P,S>;
Note that the "structure-name" is the zero-th structure
formal parameter. The formals "I", "P" and "S" are already
outside of conditional flow, so they are processed
correctly. This change will cause the compiler to use
slightly more memory, but the resulting code will be
correct. There should be no reduction in optimization
either.
Be aware that there is no problem when the conditional flow
is constant-folded at compile-time, or when there is no
conditional flow in the structure body.
10.0 KNOWN BUGS
There are no known problems with the TOPS-20 release.
11.0 FOR FURTHER HELP
A number of sources of additional help are available.
o For information on command interface -- "HLP:BLISS.HLP" Just
type "HELP BLISS" to the monitor.
o Language information -- "BLISS Language Guide": Documents
the BLISS language. The Fourth Edition, which documents
version 4 of BLISS is available as SDC order number
AA-H275C-TK, with Update Notice 1, order number AD-H275C-T1.
BLISS-36 Release 4A(236) For TOPS-20: Release Notes Page 8
o Compiler information -- "BLISS-36 User's Guide": Describes
use of the BLISS-36 compiler, some available tools, and
machine specific features. The Fourth Edition, which
documents version 4 of BLISS-36 is available as SDC order
number AA-H712D-TK.
o Syntax summary -- "BLISS Pocket Guide": Available as SDC
order number AV-AT45A-TK.
o BLISS course -- A course in the BLISS programming language is
available from DEC. For further information contact
Educational Services.
o BLISS-36 debugger (SIX12): "HLP:SIX12.HLP": Just type "HELP
SIX12" to the monitor.
o Simple terminal I/O: "HLP:TUTIO.HLP": Just type "HELP
TUTIO" to the EXEC.
o Conversion of BLISS-10 programs to BLISS-36 --
"HLP:CVT10.HLP": Just type "HELP CVT10" to the EXEC. For
greater detail see the file "DOC:CVT10.DOC".
o Monitor interfaces -- "DOC:MONINT.DOC".
o Examining ".REL" files -- "HLP:DMPREL.HLP": Just type "HELP
DMPREL" to the EXEC.
12.0 COMPONENTS
Below is a list of the major components of the BLISS-36 system.
Full support is available only for the BLISS compiler itself. The
other components are unsupported but will be maintained to the extent
our resources allow.
o BLISS -- The BLISS-36 compiler itself.
o EZIO and TUTIO -- I/O utilities for BLISS-36.
o Monitor Interfaces -- definitions necessary for interfacing
with the TOPS-10 and TOPS-20 monitors.
o CVT10 -- BLISS-10 to BLISS-36 conversion program.
o SIX12 -- High level debugger for BLISS-36.
o XPORT -- Transportable BLISS programming tools